Back Pressure....How Much Is To Much?

[one eyed willy]

No flex pipe and Borla non-chambered mufflers. They did not drop the exhaust system. Shop did not think that was the issue.

I wonder if mounting a EGT in the same spot just before entry into the turbo would work?

EGT usually has to be installed pretty close the actual cylinder to read the highest temps.

 

[Makdaddy]

EGT (exhaust gas temperature) monitoring can be a very effective tool in tuning, but "ideal" EGT can vary from engine to engine dependant upon combination. Usually, 1300 to 1500 degrees F is optimal for normally aspirated engines on gas, while gas turbos will run optimally @ 1500 to 1650. An important note: this is measured before the turbo, not after, as the turbo will reduce EGT by an average 200 degrees F.

Quoted from Hahn Racing

 

[weather man]

Well, I am very familiar with EGT's from the 2 stroke sled world. The best readings were always as close to the exhaust port as you could get.

I have PLX gauges and they make a EGT module I could daisy chain in.

The forward cylinder would probably not be to bad.

Hmmmmm...goddamn it, now I'm curious. Good head banging guys.

 

[TurboX]

Need it at the exhaust port, temps downstream can be inaccurate.

 

[retfr8flyr]

I mounted my EGT probes in the short collector just below turbo. The probes that came with my gauges wouldn't allow for mounting in an individual pipe. Here is an old pic of my original engine but it shows the EGT mounting hole.





Earl

 

[TurboX]

What kind of temps did you see Earl ?

 

[weather man]

I just did some reading that says from within 3" of head to turbo, the temp can drop 300F.

 

[rcm90]

I'm starting to think the exhaust wheel is too small.

 

[Thekid760]

x2 your turbine is likely way too small.

Per Garrett: max EBP should be 1.5-2:1, but they like it at 1-1.5:1.

Re: velocity and pipe size; per corky bell the ideal velocity to achieve is around .4 Mach. Any higher and it's a restriction, lower causes lag and turbulence. Assuming your turbos flow based on hp (690cfm or so) and using 2.5" diameter your Mach is .30. But that doesn't take into account the extra velocity from the heated gasses.


Misspelling courtesy of my fat fingers...

 

[weather man]

It is interesting that the PLX EGT install directions say 6" to 12" from engine block provides best performance.

 

[retfr8flyr]

What kind of temps did you see Earl ?

Mine run between 800-1100 for normal driving. Cruising at 75 on the highway they will be a little over 1000. At the end of a pass they will be a little over 1300.


Earl

 

[Makdaddy]

So Brian

I guess next question
If your EGT are tooo high is it lean or rich?

 

[TurboX]

Neither, the back pressure is causing heat

 

[BruceH]

Why not monitor them in obd? Or is my thinking wrong here? I'm under the impression off the top of my head that obd uses heat readings from the o2 sensors for several things in the tune. One of them is for exhaust valve protection but it's usually turned off in a custom tune. Still though, it should be able to be monitored without another sensor.

 

[weather man]

Why not monitor them in obd? Or is my thinking wrong here? I'm under the impression off the top of my head that obd uses heat readings from the o2 sensors for several things in the tune. One of them is for exhaust valve protection but it's usually turned off in a custom tune. Still though, it should be able to be monitored without another sensor.

I think getting the actual EGT vs an inferred value is what it will take to be sure Bruce. My tune does not come close to pushing lean. I think Danny stayed conservative with the back pressure in the back of his mind. Lean is mean, but it is hotter also.

 

[CPRsm]

It's not a certain ratio that will kill anything. I'm learning everyday. 2-1 is generally the cutoff for power production. But that is not always the case. There are some instances where the compressor can still stuff it in. One of my Aussie customers damn near shoots for 2-1. W his type fuel back pressure has little effect on him. Then we get to coyote stuff where there are volitile cylinders to begin with, then reversion of hot gas back into the cyl or it just never escapes. Wanna talk about seeing knock under the most gentle of conditions? Customer recently dynoed his and watched it fline in power and lb/min. Yours at least is still making power. This shit looked like a hellion single. Took off his stock damn mufflers, and BAM. Then dumped the whole exh and picked up another 53rwhp on top of it all.
Back pressure when the ratio is high can wear a turbo thrust sooner. The exh side it trying to push the turbine theu the air filter. When the ratios are closer balanced, the compressor will push back relieving pressure on the exh side of the thrust. This is where BB turbos can be nice. 2-1 does not automatically mean POP.

 

[Sprayer84]

I obviously will be following this thread very closely. What's the number 1 suspect in the back pressure being high? Will a larger, 3" up pipe fit and help reduce back pressure? I know that when I did my bp tests it pegged my 20psi gauge out running 9psi.


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[weather man]

What's the number 1 suspect in the back pressure being high?

The hotside turbine size being to small.

 

[Sprayer84]

.96 being too small? I just ordered a .81 hoping to spool faster. FUCK ME.


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[weather man]

.96 being too small? I just ordered a .81 hoping to spool faster. FUCK ME.


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COMP isn't returning my e-mails anymore.

And by small, the concensus seems to be the actual size and/or design of the turbine.

Ask them how they are helping the other guy with the same turbo who sent all requested info and shop info, who they haven't called.